Image transmitter

ABSTRACT

A transmitter is capable of compressing an incoming image with a relatively small delay time and transmit the compressed image data to a receiver. Image data contains at least i pixel values of pixels arranged in line along a single direction, each pixel value being expressed in n bits. A transmitter for compressing such image data and transmitting the image data to a receiver via a transmission path includes a blocking section, a data compression section, and a data sending section. The blocking section takes every p pixel values among the i pixel values in the image data to form a data block, and sequentially outputs a plurality of the data blocks each including the p pixel values. The data compression section reduces an amount of data from each data block outputted from the blocking section and thereby outputs a compressed block. The data sending section sends the compressed block outputted from the data compression section onto the transmission path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image transmitter, and morespecifically to an image transmitter for compressing incoming image dataand transmitting the compressed image data to a receiver via atransmission path.

2. Description of the Background Art

Examples of conventional image compression schemes are the MPEG (MotionPicture Experts Group) scheme and the DVC (Digital Video Cassette)scheme. According to these image compression schemes, incoming imagedata is subjected to DCT (Discrete Cosine Transform) and variable-lengthcoding on a macro block-by-macro block basis, whereby a high compressionrate for the image data may be realized. An implementation example ofsuch an image compression scheme is a moving picture encoder which isdisclosed in Japanese Patent Laid-Open Publication No. 7-280911.

However, after the aforementioned moving picture encoder receives oneline of pixels arranged along a horizontal direction within an image tobe processed, the moving picture encoder may also receive a next line ofpixels. As a result, before all of the pixels which compose one macroblock are received, the moving picture encoder may receive a number ofpixels which are unrelated to that macro block. The receipt of suchunnecessary pixels causes a delay time associated with compressionprocessing in conventional moving picture encoders.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide atransmitter which is capable of compressing an incoming image fortransmission to a receiver with a relatively small delay time.

The present invention has the following features to attain the objectabove. According to one aspect of the invention, there is provided animage transmitter for compressing image data and transmitting the imagedata to a receiver via a transmission path, wherein the image data atleast contains i pixel values of pixels arranged in line along a singledirection, each pixel value being expressed in n bits, the imagetransmitter comprising: a blocking section for taking every p pixelvalues among the i pixel values in the image data to form a data block,and sequentially outputting a plurality of the data blocks eachincluding the p pixel values; a data compression section for reducing anamount of data from each data block outputted from the blocking sectionto output a compressed block; and a data sending section for sending thecompressed block outputted from the data compression section onto thetransmission path, wherein i, n, and p are predetermined naturalnumbers.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a structure of an imagetransmitter Tx according to one embodiment of the present invention;

FIGS. 2A and 2B are diagrams illustrating an image MG represented byimage data TD which is received by a blocking section 1 shown in FIG. 1;

FIG. 3 is a diagram illustrating a format of the image data TD which isreceived by the blocking section 1 shown in FIG. 1;

FIG. 4 is a diagram illustrating a format of data block DB_(r) which isoutputted from the blocking section 1 shown in FIG. 1;

FIG. 5 is a block diagram illustrating a first implementation (a “datacompression section 2 a”) of a data compression section 2 shown in FIG.1;

FIG. 6 is a block diagram illustrating the detailed structure of a DPCMencoding section 22 shown in FIG. 5;

FIG. 7 is a block diagram illustrating the detailed structure of anear-instantaneous compression section 23 shown in FIG. 5;

FIG. 8 is a diagram illustrating a format of differential dataDD_(p×(r−1)+2) to DD_(p×r) which are outputted from the a format of theDPCM encoding section 22 shown in FIG. 5;

FIG. 9 is a diagram illustrating bit patterns BP₁ to BP_(n) of maximumdifferential data MDD_(v) to be selected by a differential dataselection section 2321 shown in FIG. 7;

FIG. 10 is a table illustrating the relationship between bit patternsBP₁ to BP_(n) shown in FIG. 9 and level values LV₁ to LV_(t+1);

FIG. 11 is a diagram illustrating a format of compressed differentialdata CDD_(p×(r−1)+2) to CDD_(p×r) which are outputted from a datareduction section 233 shown in FIG. 7;

FIG. 12 is a diagram illustrating an exemplary relationship between thelevel values LV₁ to LV_(t+1) shown in FIG. 10 and the bits to be deletedfrom the differential data DD_(p×(r−1)+2) to DD_(p×r);

FIG. 13 is a diagram illustrating another exemplary relationship betweenthe level values LV₁ to LV_(t+1) shown in FIG. 10 and the bits to bedeleted from the differential data DD_(p×(r−1)+2) to DD_(p×r);

FIG. 14 is a diagram illustrating a format of data packet DP_(r) whichis outputted from a packet assembling section 24 shown in FIG. 5;

FIG. 15 is a block diagram illustrating a first implementation (a“receiver Rxa”) of a receiver Rx shown in FIG. 1;

FIG. 16 is a block diagram illustrating the detailed structure of adecompression/decoding section 7 shown in FIG. 15;

FIG. 17 is a block diagram illustrating the detailed structure of a DPCMdecoding section 72 shown in FIG. 15;

FIGS. 18A and 18B are diagrams illustrating the processing to beperformed by a near-instantaneous decompression section 71 shown in FIG.16 responsive to the level value LV₁;

FIGS. 19A and 19B are diagrams illustrating the processing to beperformed by the near-instantaneous decompression section 71 shown inFIG. 16 responsive to the level value LV₂;

FIG. 20 is a diagram illustrating a format of reproduced image data RTDto be reproduced by an image data reproduction section 8 shown in FIG.15;

FIG. 21 is a diagram illustrating the generation of padded data blockPDB performed by the blocking section 1;

FIG. 22 is a block diagram illustrating a variant (a “data compressionsection 2 b”) of the data compression section 2 a shown in FIG. 5;

FIG. 23 is a block diagram illustrating the detailed structure of a DPCMencoding section 25 shown in FIG. 22;

FIG. 24 is a block diagram illustrating the structure of a variant(“receiver Rxb”) of the receiver Rxa shown in FIG. 15;

FIG. 25 is a diagram illustrating an exemplary process performed by amissing block recovery section 9 shown in FIG. 24;

FIG. 26 is a block diagram illustrating a second implementation (a “datacompression section 2 c”) of the data compression section 2 shown inFIG. 1;

FIG. 27 is a diagram illustrating a format of coefficientsCF_(p×(r−1)+1) to CF_(p×r) which are outputted from an orthogonaltransform section 26 shown in FIG. 26;

FIG. 28 is a diagram illustrating a portion of the process performed bya data reduction section 27 shown in FIG. 26;

FIG. 29 is a diagram illustrating the rest of the process performed bythe data reduction section 27 shown in FIG. 26;

FIG. 30 is a block diagram illustrating a second implementation (a“receiver Rxc”) of the receiver Rx shown in FIG. 1;

FIG. 31 is a block diagram illustrating the overall configuration of adriving assistant system TS₁ incorporating transmitters Tx and receiverRx as shown in FIG. 1;

FIG. 32 is a diagram illustrating a process performed by the drivingassistant system TS₁ shown in FIG. 31;

FIG. 33 is a schematic diagram illustrating technological effectsassociated with the driving assistant system TS₁ shown in FIG. 31; and

FIG. 34 is a block diagram illustrating the overall structure of aremote control system TS₂ incorporating a transmitter Tx and a receiverRx as shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram illustrating an overall structure of an imagetransmitter Tx according to one embodiment of the present invention. Asshown in FIG. 1, the image transmitter Tx is constructed so as to becapable of data communication with a receiver Rx via a transmission pathN, and includes a blocking section 1, a data compression section 2, anda data sending section 3. The transmission path N may be wired orwireless.

The blocking section 1 receives image data TD to be processed. As shownin FIG. 2A, the image data TD typically represents one frame of imageMG. In FIG. 2A, the image MG is composed of (i×j) pixels PE. Herein, “i”and “j” are predetermined natural numbers, which in the presentembodiment are assumed to be 640 and 480, respectively. Morespecifically, the image MG has a width equal to i pixels PE along awidth (horizontal) direction HD. The image MG has a length equal to jpixels PE along a longitudinal (vertical) direction VD, the longitudinaldirection VD running perpendicular to the width direction HD. Althoughonly one pixel PE (a rectangular region which is shown hatched) islabeled as “PE” in FIG. 2A for conciseness, it will be appreciated thateach rectangular region in the image MG represents a pixel PE. FIG. 2Aalso shows that the value of each pixel PE is expressed in an n-bitbinary format. Herein, “n” is a predetermined natural number, which inthe present embodiment is assumed to be 8. In the following description,the value of each pixel PE will be referred to as a “pixel value XV”.

As shown in FIG. 2B, a pixel PE in the image MG which is located at ak^(th) position along the width direction HD and at an m^(th) positionalong the longitudinal direction VD will conveniently be expressed as a“pixel PE_(j×(m−1)+k)”, whose value will be expressed as a “pixel valueXV_(j×(m−1)+k)”. Herein, “k” is a natural number such that 1≦k≦i; and“m” is a natural number such that 1≦m≦j. The suffix “i×(m−1)+k” for thereference numeral “PF” represents an order by which the blocking section1 receives the respective pixels PE. For example, under the aboveassumption where the image MG is composed of 640×480 pixels PE, a pixelPE which is located at the first position along the width direction HDand at the first position along the longitudinal direction VD will berepresented as a “pixel PE₁”. Similarly, a pixel PE which is located atthe 100^(th) position along the width direction HD and at the 121^(st)position along the longitudinal direction VD will be represented as a“pixel PE₇₆₉₀₀”. Similarly, the last pixel PE, or a pixel which islocated at the 640^(th) position along the width direction HD and at the480^(th) position along the longitudinal direction VD, will berepresented as a “pixel PE₃₀₇₂₀₀”.

As shown in FIG. 3, the image data TD which is received by the blockingsection 1 has a format such that the image data TD is composed of (i×j)pixel values XV_(i×(m−1)+k) (m=1,2, . . . j, k=1,2, . . . i), that is,the image data TD is a collection of pixel values XV₁ to XV_(i×j). Morespecifically, in the image data TD, the pixel value XV₁ is located atthe beginning, immediately followed by a pixel value XV₂. In turn, thepixel value XV₂ is followed by pixel values XV₃ to XV_(i), which composethe rest of the first line along the width direction HD. Then comes asecond line of pixel values XV_(i+1), followed by pixel values XV_(i+2)to XV_(2×i). Similarly, third, fourth, . . . , and j^(th) lines of pixelvalues XV_(2×i+1) to XV_(3×i), pixel values XV_(3×i+1) to XV_(4×i), . .. and pixel values XV_(i×(j−1)+1) to XV_(i×j) respectively follow.

In addition to the pixel values XV₁ to XV_(i×j), the image data TD maycontain any other additional information to be used for certainpurposes. However, such additional information is not essential for thepresent embodiment of the invention, and therefore is omitted from theillustration and descriptions.

In accordance with the aforementioned format of the image data TD, theblocking section 1 receives the pixel values XV₁ to XV_(i×j) in thisorder. Among the incoming pixel values XV₁ to XV_(i×j), the blockingsection 1 takes every p (where p is a predetermined number) pixel valuesto generate q data blocks DB, each of which is composed of p pixelvalues. Herein, “p” is a divisor of i, and in the present embodiment isassumed to be 8; and “q” is equal to {(i×j)/p}. Under the aboveassumptions where i=640, j=480, and p=8, q is 38400. For conciseness, adata block DB which is the r^(th) generated data block will be denotedas a “data block DB_(r)” with a suffix r. Herein, “r” is a naturalnumber such that 1≦r≦q. As shown in FIG. 4, such a data block DB_(r)(r=1,2, . . . q) will be a collection of p pixel values XV_(p×(r−1)+1)to XV_(p×r). Under the above assumptions, the first generated data blockDB₁ is a collection of pixel values XV₁ to XV₈, given that r=1.Similarly, the second data block DB₂ is composed of pixel values XV₉ toXV₁₆. The last generated data block DB₃₈₄₀₀ is composed of pixel valuesXV307192 to XV₃₀₇₂₀₀. Such data blocks DB_(r) are outputted from theblocking section 1 to the data compression section 2 in the order inwhich they are generated (see FIG. 1).

As described in connection with the background art, according to thetypical conventional image compression schemes such as the MPEG schemeor the DVC scheme, a number of unnecessary pixels are likely to havebeen received before all of the pixels composing a macro block arereceived, giving rise to an unwanted delay time. In contrast, accordingto the present embodiment of the invention, the blocking section 1generates a data block DB_(r) which is composed of p pixel values XV₁ toXV_(i×j) in the order they are received. In other words, the blockingsection 1 becomes ready to construct a data block DB_(r) as soon as itreceives p contiguous pixel values XV along the width direction HD,which can then be quickly passed to the next stage, i.e., the datacompression section 2. As a result, the delay time can be reduced ascompared to the conventional image compression schemes.

The data compression section 2 performs a first or second compressionprocess (described later) for each incoming data block DB_(r). Thus, thedata compression section 2 generates a compressed block CB_(r) (r=1,2, .. . q) having a fixed length composed of predetermined s bits. Eachcompressed block CB_(r) thus generated is outputted from the datacompression section 2 to the data sending section 3 (see FIG. 1).

Next, with reference to FIGS. 5 to 7, a first exemplary implementationof the data compression section 2 shown in FIG. 1 will be described. Inthe following description, the first implementation of the datacompression section 2 will be referred to as a “data compression section2 a”. As shown in FIG. 5, in order to realize the aforementioned firstcompression process, the data compression section 2 a includes asplitter section 21, a DPCM encoding section 22, a near-instantaneouscompression section 23, and a packet assembling section 24. Asspecifically shown in FIG. 6, the DPCM encoding section 22 of FIG. 5includes a delay section 221 and a subtraction section 222. Asspecifically shown in FIG. 7, the near-instantaneous compression section23 shown in FIG. 5 includes a buffer section 231, a level determinationsection 232, and a data reduction section 233.

Next, the first compression process which is performed by the datacompression section 2 a having the above-described structure will bespecifically described. Data blocks DB_(r) which are sent from theblocking section 1 (described above) are sequentially received by thesplitter section 21 in the data compression section 2 a. Each data blockDB_(r) includes an array of p pixel values XV_(p×(r−1)+1) to XV_(p×r)(see FIG. 4). As shown in FIG. 6, as each data block DB_(r) is received,the splitter section 21 outputs the pixel value XV_(p×(r−1)+1), which islocated at the beginning of the received data block DB_(r), to both thepacket assembling section 24 and the delay section 221. Moreover, thesplitter section 21 outputs each of the pixel values XV_(p×(r−1)+2) toXV_(p×r−1) to both the delay section 221 and the subtraction section222. Furthermore, the splitter section 21 outputs a p^(th) pixel valueXV_(p×r) to the subtraction section 222.

As shown in FIG. 6, the DPCM encoding section 22 receives pixel valuesXV_(p×(r−1)+1) to XV_(p×r). The DPCM encoding section 22 performs adifferential pulse code modulation (Differential Pulse Code Modulation)to encode each of the received pixel values XV_(p×(r−1)+2) to XV_(p×r),thereby generating differential data DD_(p×(r−1)+2) to DD_(p×r), whichare then outputted to the near-instantaneous compression section 23.

More specifically, the delay section 221 sequentially receives pixelvalues XV_(p×(r−1)+1) to XV_(p×r−1). The delay section 221 applies adelay amount DL₁ to the respective received pixel values XV_(p×(r−1)+1)to XV_(p×r−1), and outputs the resultant pixel values as delayed pixelvalues LXV_(p×(r−1)+1) to LXV_(p×r−1) to the subtraction section 222.Now, the delay amount DL₁ will be specifically described. Thesubtraction section 222 receives (as described later) pixel valuesXV_(p×(r−1)+2) to XV_(p×r) from the splitter section 21. The delayamount DL₁ is prescribed at a value which ensures that the delayed pixelvalues LXV_(p×(r−1)+1) to LXV_(p×r−1) will be received by thesubtraction section 222 substantially concurrently with the pixel valuesXV_(p×(r−1)+2) to XV_(p×r). In the present embodiment of the invention,the delay amount DL₁ is prescribed to be equal to one clock whichdefines the operation timing of the DPCM encoding section 22.

The subtraction section 222 receives the pixel values XV_(p×(r−1)+2) toXV_(p×r) from the splitter section 21. The subtraction section 222 alsoreceives the delayed pixel values LXV_(p×(r−1)+1) to LXV_(p×r−1) fromthe delay section 221. Note that the aforementioned delay amount DL₁ensures that the delayed pixel value LXV_(p×(r−1)+1) from the delaysection 221 and the pixel value XV_(p×(r−1)+2) from the splitter section21 are received by the subtraction section 222 substantiallysimultaneously. The subtraction section 222 subtracts thecurrently-received delayed pixel value LXV_(p×(r−1)+1) from thecurrently-received pixel value XV_(p×(r−1)+2) to generate a differentialdata DD_(p×(r−1)+2) representing a difference value therebetween. Inother words, the subtraction section 222 calculates a difference valuebetween the received pixel value XV_(p×(r−1)+2) and a preceding pixelvalue XV_(p×(r−1)−1) in the image data TD (see FIG. 2B). This differencevalue may take a positive or negative value. Accordingly, as shown inFIG. 8, a sign bit SB_(p×(r−1)+2), which is a one-bit expression of thesign (i.e., positive or negative) of the difference value, is added tothe differential data DD_(p×(r−1)+2) as its most significant bit(hereinafter referred to as the “MSB”). In the present embodiment of theinvention, it is assumed that the sign bit SB_(p×(r−1)+2) is “0” whenthe difference value is positive, and “1” when the difference value isnegative. The sign bit SB_(p×(r−1)+2) is followed by an n-bit expressionof the absolute value of the difference value AV_(p×(r−1)+2) (=|pixelvalue XV_(p×(r−1)+2)−pixel value XV_(p×(r−1)+1)|). Thus, thedifferential data DD_(p×(r−1)+2) is composed of (n+1) bits.

Moreover, the subtraction section 222 subtracts the delayed pixel valueLXV_(p×(r−1)+2) from the concurrently-received pixel valueXV_(p×(r−1)+3) to generate a differential data DD_(p×(r−1)+3).Thereafter, the subtraction section 222 repeats similar processes untilit generates a differential data DD_(p×r) from the pixel value XV_(p×r)and the delayed pixel value LXV_(p×r−1). As can be seen from FIG. 8, thedifferential data DD_(p×(r−1)+3) to DD_(p×r) have a format which issimilar to that of the differential data DD_(p×(r−1)+2). As shown inFIG. 6, the subtraction section 222 sequentially outputs the generateddifferential data DD_(p×(r−1)+2) to DD_(p×r) to the near-instantaneouscompression section 23.

As described above, q data blocks DB_(r) are generated for one frame ofimage MG, and the DPCM encoding section 22 generates differential dataDD_(p×(r−1)+2) to DD_(p×r) for each data block DB_(r). Therefore, thenear-instantaneous compression section 23 sequentially receives q setsof differential data DD_(p×(r−1)+2) to DD_(p×r). The near-instantaneouscompression section 23 generates compressed data CD_(p×(r−1)+2) toCD_(p×r) from each set of received differential data DD_(p×(r−1)+2) toDD_(p×r), respectively, in accordance with a near-instantaneouscompression scheme.

More specifically, the buffer section 231 shown in FIG. 7, which isconstructed so as to be capable of storing (p−1)×(n+1) bits of data,stores the differential data DD_(p×(r−1)+2) to DD_(p×r) from thesubtraction section 222. The buffer section 231 outputs the storeddifferential data DD_(p×(r−1)+2) to DD_(p×r) to both the leveldetermination section 232 and the data reduction section 233.

The level determination section 232 generates one level value LV_(r) forevery set of differential data DD_(p×(r−1)+2) to DD_(p×r) received fromthe buffer section 231. The data reduction section 233 deletespredetermined t bits from each of the received differential dataDD_(p×(r−1)+2) to DD_(p×r), as will be described in more detail later.Herein, “t” is a natural number such that 1≦t<(n+1), and in the presentembodiment is assumed to be 5. Stated differently, the data reductionsection 233 leaves u bits intact among the (n+1) bits which compose eachof the differential data DD_(p×(r−1)+2) to DD_(p×r). Herein, “u” isequal to (n+1−t), which under the above assumptions is 4. The levelvalue LV_(r) specifies the positions of the u bits to be left intactamong the (n+1) bits which compose each of the differential dataDD_(p×(r−1)+2) to DD_(p×r).

In order to derive the aforementioned level value LV_(r), the leveldetermination section 232 shown in FIG. 7 includes a differential dataselection section 2321 and a level selection section 2322. Thedifferential data selection section 2321 receives the differential dataDD_(p×(r−1)+2) to DD_(p×r) (see FIG. 8) from the buffer section 231. Thedifferential data selection section 2321 selects one of the differentialdata DD_(p×(r−1)+2) to DD_(p×r) having the greatest absolute valuesAV_(p×(r−1)+2) to AV_(p×r−1), and outputs that differential data to thelevel selection section 2322. In the following description, thedifferential data which is thus selected by the differential dataselection section 2321 will be referred to as the “maximum differentialdata MDD_(v)”. Herein, “v” is a natural number in the range from{p×(r−1)+2} to p×r.

The level selection section 2322 receives the maximum differential dataMDD_(v) from the differential data selection section 2321. The levelselection section 2322 determines the sign (i.e., positive or negative)of the received maximum differential data MDD_(v) based on the value ofits sign bit SB_(v).

If the current maximum differential data MDD_(v) has a positive value(i.e., the sign bit SB_(v) is “0”), then the level selection section2322 operates in the following manner. Herein, in the case where thesign bit SB_(v) is “0”, the maximum differential data MDD_(v) has one ofn bit patterns BP₁ to BP_(n) as shown in FIG. 9. As shown, the bitpattern BP₁ is a bit pattern in which the first instance of “1” appearsnext to the sign bit SB_(v), i.e., at the second bit from the MSB.Similarly, the bit patterns BP₂ to BP_(n) are bit patterns in which thefirst instance of “1” appears at the third to (n+1)^(th) bits from theMSB, respectively. In FIG. 9, any bit shown by the symbol “−” may takeeither “0” or “1”. In the following description, in the positive maximumdifferential data MDD_(v), the bit position at which the first instanceof “1” appears (i.e., one of the second to the (n+1)^(th) bits), ascounted from the MSB, will be referred to as a “reference bit position”RBL₁ to RBL_(n).

In the present embodiment of the invention, as shown in FIG. 10, (t+1)level values LV₁ to LV_(t+1) are previously assigned to the bit patternsBP₁ to BP_(n) in the following manner. As described above, “t”represents the number of bits to be deleted from each of thedifferential data DD_(p×(r−1)+2) to DD_(p×r), which in the presentembodiment is assumed to be 5. Specifically, level values LV₁ to LV_(t)are assigned to the bit patterns BP₁ to BP_(t), respectively. The samelevel value LV_(t+1) is assigned to all of the bit patterns BP_(t+1) toBP_(n). In other words, the respective level values LV₁ to LV_(t) areassigned to the reference bit positions RBL₁ to RBL_(t), whereas thesame level value LV_(t+1) is assigned to the reference bit positionsRBL_(t+1) to RBL_(n).

In the following description, as shown in FIG. 10, the bit patternBP_(w) is one of the bit patterns BP₁ to BP_(n). Similarly, thereference bit position RBL_(w) is one of the reference bit positionsRBL₁ to RBL_(n). In other words, w is a natural number in the range from1 to n. The level value LV_(y) is one of the level values LV₁ toLV_(t+1), and is expressed in z bits; y is a natural number in the rangefrom 1 to (t+1); and z is the number of digits which are required whenconverting (t+1) into a binary expression. Preferably, the value of z isas small as possible. For example, when t=5, z is most preferably 3.

The level selection section 2322 detects the bit position at which thefirst instance of “1” appears, the check being begun at the MSB of thecurrent maximum differential data MDD_(v). In other words, the levelselection section 2322 determines one of the reference bit positionsRBL₁ to RBL_(n) which corresponds to the current maximum differentialdata MDD_(v). Next, the level selection section 2322 selects one of thelevel values LV₁ to LV_(t+1) which is assigned to thecurrently-determined one of the reference bit positions RBL₁ to RBL_(n),and outputs this level value to both the data reduction section 233 andthe packet assembling section 24. Among the level values LV₁ toLV_(t+1), the currently-outputted level value is referred to as the“level value LV_(y)”, as defined earlier.

As described above, the data reduction section 233 receives thedifferential data DD_(p×(r−1)+2) to DD_(p×r) from the buffer section231. The data reduction section 223 also receives the level value LV_(y)from the level determination section 232. Based on the current levelvalue LV_(y), the data reduction section 233 deletes t bits from each ofthe current differential data DD_(p×(r−1)+2) to DD_(p×r). As a result,as shown in FIG. 11, the data reduction section 233 generates compresseddifferential data CDD_(p×(r−1)+2) to CDD_(p×r), each of which iscomposed of u bits.

According to the present embodiment of the invention, as shown in FIG.12, the bits to be deleted from the current differential dataDD_(p×(r−1)+2) to DD_(p×r) are predetermined for each of theaforementioned level values LV₁ to LV_(t+1). For the sake ofillustration, FIG. 12 shows an exemplary case in which n=8, t=5, andu=4. Specifically, regardless of which one of the level values LV₁ toLV_(t+1) is currently received, the data reduction section 233 leavesintact (i.e., without deleting) the sign bits SB_(p×(r−1)+2) to SB_(p×r)of all differential data DD_(p×(r−1)+2) to DD_(p×r). When the levelvalue LV₁ is received, the data reduction section 233 leaves intact theaforementioned reference bit position RBL₁ and the following (u−2) bits(i.e., the (u−2) bits immediately on the lower side) contained in eachof the differential data DD_(p×(r−1)+2) to DD_(p×r), while deleting theother t bits. Similarly, when one of the level values LV₂ to LV_(t) isreceived, the data reduction section 233 leaves intact theaforementioned reference bit positions RBL₂ to RBL_(t) and the following(u−2) bits in each of the differential data DD_(p×(r−1)+2) to DD_(p×r).When the level value LV_(t+1) is received, the data reduction section233 leaves intact the lower (u−1) bits in each of the differential dataDD_(p×(r−1)+2) to DD_(p×r), while deleting the second to (u−2)^(th) bitsas counted from the MSB.

As mentioned earlier, it is assumed that the sign bits SB_(p×(r−1)+2) toSB_(p×r) are “0”. Under this assumption, the data reduction section 233may alternatively operate in the manner shown in FIG. 13, so that whenone of the level values LV₁ to LV_(t) is received, the data reductionsection 233 simply leaves intact the reference bit positions RBL₂ toRBL_(t) as well as its preceding bit and the following (u−2) bits ineach of the differential data DD_(p×(r−1)+2) to DD_(p×r). When the levelvalue LV_(t+1) is received, the lower u bits are left intact in each ofthe differential data DD_(p×(r−1)+2) to DD_(p×r). Note that theoperation scheme of FIG. 13 is directed to the same exemplary case whichFIG. 12 is drawn to, i.e., n=8, t=5, and u=4.

Thus, the data reduction section 233 deletes t bits from each of thecurrently-received differential data DD_(p×(r−1)+2) to DD_(p×r) togenerate compressed differential data CDD_(p×(r−1)+2) to CDD_(p×r), eachof which is composed of u bits. The respective generated compresseddifferential data CDD_(p×(r−1)+2) to CDD_(p×r) are outputted to thepacket assembling section 24.

The above description illustrates the case where the sign bitsSB_(p×(r−1)+2) to SB_(p×r) are “0”. On the other hand, in the case wherethe sign bits SB_(p×(r−1)+2) to SB_(p×r) are “1”, the level selectionsection 2322 detects the reference bit position at which the firstinstance of “0” appears, as counted from the MSB of thecurrently-received maximum differential data MDD_(v). Furthermore, thelevel selection section 2322 selects one of the level values LV₁ toLV_(t+1) which is assigned to the currently-determined reference bitposition, and outputs this level value to both the data reductionsection 233 and the packet assembling section 24.

As mentioned earlier, the packet assembling section 24 receives thepixel value XV_(p×(r−1)+1) from the splitter section 21 as well as thelevel value LV_(y) from the level determination section 232. The packetassembling section 24 also receives the compressed differential dataCDD_(p×(r−1)+2) to CDD_(p×r) from the data reduction section 233. Basedon these received data, the packet assembling section 24 assembles adata packet DP_(r) as shown in FIG. 14. As shown in FIG. 14, theassembled data packet DP_(r) contains the pixel value XV_(p×(r−1)+1),the level value LV_(y), and the compressed differential dataCDD_(p×(r−1)+2) to CDD_(p×r), and has a fixed length of {(n+z+u×(n−1)}bits. The packet assembling section 24 outputs the assembled data packetDP_(r) to the data sending section 3 as the aforementioned compressedblock CB_(r) (see FIG. 1).

As shown in FIG. 1, the data sending section 3 includes a buffer section31 and a sending control section 32. The buffer section 31 stores thefixed-length data packet DP_(r). Since typical conventional imagecompression schemes such as the MPEG scheme or the DVC scheme perform avariable-length coding, a large-capacity transmission buffer isinevitably required. The use of such a large-capacity transmissionbuffer for buffering variable-length encoded data may introduce asubstantial delay time in the conventional image compression schemes. Incontrast, according to the present embodiment of the invention, thebuffer section 31 only needs to store the fixed-length data packetDP_(r), so that the delay time associated with the buffering which takesplace in the buffer section 31 is minimized, and the delay time becomessubstantially constant for every data packet DP_(r). Thus, the use offixed-length data packet DP_(r) also serves to reduce the delay timerelative to that which is associated with the conventional imagecompression schemes.

After the data packet DP_(r) is stored in the buffer section 31, thesending control section 32 receives the data packet DP_(r) from thebuffer section 31 and sends it onto the transmission path N. The datapacket DP_(r), as an example of compressed data CD_(r), is transmittedthrough the transmission path N and then received by the receiver Rx, asshown in FIG. 1.

The receiver Rx subjects the received data packet DP_(r) topredetermined processing. Hereinafter, with reference to FIG. 15 to FIG.17, a first implementation of the receiver Rx shown in FIG. 1 will bedescribed. In the following description, the first implementation of thereceiver Rx will be referred to as a “receiver Rxa”. As shown in FIG.15, in order to realize reproduction processing for the image data TD,the receiver Rxa includes a data receiving section 5, a packetdeassembling (disassembling) section 6, a decompression/decoding section7, and an image data reproduction section 8. The data receiving section5 includes a buffer section 51 and a reception control section 52. Asshown in FIG. 16, the decompression/decoding section 7 includes anear-instantaneous decompression section 71 and a DPCM decoding section72. As shown in FIG. 17, the DPCM decoding section 72 includes a delaysection 721 and an adder section 722.

Next, the reproduction processing for the image data TD which isperformed by the receiver Rxa will be described in detail. The datapackets DP_(r) from the transmission path N are sequentially received bythe receiving section 5. In the receiving section 5, the buffer section51 stores the data packet DP_(r). The buffer section 51, which is onlyrequired to store the fixed-length data packets DP_(r), as is the casewith the buffer section 31, contributes to the minimization of the delaytime. After the buffering, the reception control section 52 receives thedata packet DP_(r) from the buffer section 51, and outputs the datapacket DP_(r) to the packet deassembling section 6.

As described above, the data packet DP_(r) contains the pixel valueXV_(p×(r−1)+1), the level value LV_(y), and the compressed differentialdata CDD_(p×(r−1)+2) to CDD_(p×r) (see FIG. 14). For every received datapacket DP_(r), the packet deassembling section 6 performs a deassemblingprocess, and, as shown in FIG. 15, outputs the pixel valueXV_(p×(r−1)+1) which is located at the beginning of the received datapacket DP_(r) to the image data reproduction section 8, and outputs thepixel value XV_(p×(r−1)+1), the level value LV_(y), and the compresseddifferential data CDD_(p×(r−1)+2) to CDD_(p×r) to thedecompression/decoding section 7. To describe the outputting to thedecompression/decoding section 7 more specifically, as shown in FIG. 16,the packet deassembling section 6 sequentially outputs the level valueLV_(y) and the compressed differential data CDD_(p×(r−1)+2) to CDD_(p×r)to the near-instantaneous decompression section 71. Furthermore, asshown in FIG. 17, the packet deassembling section 6 outputs the pixelvalue XV_(p×(r−1)+1) to the delay section 721.

As described earlier, the decompression/decoding section 7 receives thepixel value XV_(p×(r−1)+1), the level value LV_(y), and the compresseddifferential data CDD_(p×(r−1)+2) to CDD_(p×r), as shown in FIG. 15. Thedecompression/decoding section 7 employs the received pixel valueXV_(p×(r−1)+1) and the level value LV_(y) to perform adecompression/decoding process for the compressed differential dataCDD_(p×(r−1)+2) to CDD_(p×r), thereby generating decoded pixel valuesDXV_(p×(r−1)+2) to DXV_(p×r) which can be regarded as substantially thesame as the aforementioned pixel values XV_(p×(r−1)+2) to XV_(p×r).

More specifically, the near-instantaneous decompression section 71 inthe decompression/decoding section 7 receives the level value LV_(y) andthe compressed differential data CDD_(p×(r−1)+2) to CDD_(p×r). Thenear-instantaneous decompression section 71 performs anear-instantaneous decompression to decompress the compresseddifferential data CDD_(p×(r−1)+2) to CDD_(p×r) based on the receivedlevel value LV_(y). Thus, the near-instantaneous decompression section71 generates decompressed differential data DDD_(p×(r−1)+2) toDDD_(p×r), which are sequentially outputted to the adder section 722.

To describe the above process more specifically, the near-instantaneousdecompression section 71 recognizes the reference bit position RBL_(w)in the received level value LV_(y). Specifically, as can be seen fromFIG. 10, one of the reference bit position RBL₁ to the reference bitposition RBL_(t) will be recognized in the case where y is in the rangefrom 1 to t. In the case where y=t+1, the near-instantaneousdecompression section 71 will recognize one of the reference bitpositions RBL_(t+1) to RBL_(n).

Once the reference bit position RBL_(w) is determined, thenear-instantaneous decompression section 71 knows the bit positionswhich were deleted from the differential data DD_(p×(r−1)+2) to DD_(p×r)in the transmitter Tx. More specifically, as can be seen from FIG. 12 orFIG. 13, when the level value LV₁ is received, the near-instantaneousdecompression section 71 recognizes that t bits have been deleted fromthe differential data DD_(p×(r−1)+2) to DD_(p×r) while leaving intactthe MSB (i.e., sign bits SB_(p×(r−1)+2) to SB_(p×r)), the reference bitposition RBL₁, and the following (u−2) bits. Similarly, when the levelvalues LV₂ to LV_(t) are received, the near-instantaneous decompressionsection 71 recognizes that t bits have been deleted from thedifferential data DD_(p×(r−1)+2) to DD_(p×r) while leaving intact therespective MSBs, the aforementioned respective reference bit positionsRBL₂ to RBL_(t), and the following (u−2) bits. When the level valueLV_(t+1) is received, the near-instantaneous decompression section 71recognizes that the second to (u−2)^(th) bits as counted from the MSBhave been deleted from each of the differential data DD_(p×(r−1)+2) toDD_(p×r).

Having thus determined the deleted bit positions, the near-instantaneousdecompression section 71 adds a bit(s) of predetermined values to eachof the compressed differential data CDD_(p×(r−1)+2) to CDD_(p×r),thereby generating the decompressed differential data DDD_(p×(r−1)+2) toDDD_(p×r), which can be regarded as substantially the same as theaforementioned differential data DD_(p×(r−1)+2) to DD_(p×r).

More specifically, when receiving the level value LV₁, as shown in FIGS.18A and 18B, the near-instantaneous decompression section 71 adds a bitsequence BS₁₁ or bit sequence BS₁₂ immediately after each of thecompressed differential data CDD_(p×(r−1)+2) to CDD_(p×r). The bitsequences BS₁₁ and BS₁₂ each have a predetermined bit pattern composedof t bits. Note that the bit sequences BS₁₁ and BS₁₂ shown in FIGS. 18Aand 18B are directed to the same exemplary case which FIG. 12 is drawnto, i.e., n=8, t=5, and u=4. As shown in FIG. 18A, the bit sequenceBS₁₁, whose first bit is “1” and other (t−1) bits are “0”, is added tothose compressed differential data CDD_(p×(r−1)+2) to CDD_(p×r) whichhave positive values. On the other hand, the bit sequence BS₁₂, whichhas a reversed bit pattern (i.e., the first bit of the bit sequence BS₁₂is “0” and the other (t−1) bits are “1”) relative to the bit sequenceBS₁₁, is added to those compressed differential data CDD_(p×(r−1)+2) toCDD_(p×r) which have negative values. Thus, the decompresseddifferential data DDD_(p×(r−1)+2) to DDD_(p×r) are generated. The bitpatterns of the bit sequences BS₁₁ and BS₁₂ are prescribed as above inorder to ensure that the differences between the values of thedecompressed differential data DDD_(p×(r−1)+2) and the values of theircorresponding original differential data DD_(p×(r−1)+2) are small.

When receiving the level value LV₂, as shown in FIG. 19A, thenear-instantaneous decompression section 71 places the MSBs of therespective compressed differential data CDD_(p×(r−1)+2) to CDD_(p×r) atthe first bit, while placing the other (u−1) bits at the third bit(i.e., the reference bit position RBL₂) through the (u+1)^(th) bit.Furthermore, for those compressed differential data CDD_(p×(r−1)+2) toCDD_(p×r) which have positive values, the near-instantaneousdecompression section 71 adds “0” at the second bit, while adding a bitsequence BS₂₁ composed of (t−1) bits at the (u+2)^(th) through n^(th)bits. Note that the bit sequence BS₂₁ is a sequence in which the onlyinstance of “1” is at the first bit, as in the bit sequence BS₁₁. On theother hand, for those compressed differential data CDD_(p×(r−1)+2) toCDD_(p×r) which have negative values, as shown in FIG. 19B, thenear-instantaneous decompression section 71 adds “1” at the second bit,while adding a bit sequence BS₂₂ composed of (t−1) bits at the(u+2)^(th) through n^(th) bits. Note that the bit sequence BS₂₂ is asequence in which the only instance of “0” is at the first bit.

Thereafter, when the level values LV₃ to LV_(t) are received, similarlyto when the level value LV₂ is received, the near-instantaneousdecompression section 71 places the MSBs of the respective compresseddifferential data CDD_(p×(r−1)+2), CDD_(p×(r−1)+3), . . . CDD_(p×r) atthe first bit, while placing the other (u−1) bits at the reference bitpositions RBL₃, RBL₄, . . . RBL_(t) through the (u+1)^(th) bit.Furthermore, for those compressed differential data CDD_(p×(r−1)+2),CDD_(p×(r−1)+3), . . . CDD_(p×r) which have positive values, thenear-instantaneous decompression section 71 sets “0” at the second bitthrough the bit immediately before the reference bit positions RBL₃,RBL₄, . . . RBL_(t), “1” at the (u+2)^(th) bit, and “0” at the(u+3)^(th) through n^(th) bits. For those compressed differential dataCDD_(p×(r−1)+2), CDD_(p×(r−1)+3), . . . CDD_(p×r) which have negativevalues, bits which are reverses of those set for the compresseddifferential data having positive values are set. As shown in FIG. 16,the decompressed differential data DDD_(p×(r−1)+2) to DDD_(p×r) whichhave been thus generated are outputted to the adder section 722 in theDPCM decoding section 72.

As shown in FIG. 16, the DPCM decoding section 72 receives the pixelvalue XV_(p×(r−1)+1) from the packet deassembling section 6 and thedecompressed differential data DDD_(p×(r−1)+2) to DDD_(p×r) from thenear-instantaneous decompression section 71. The DPCM decoding section72 performs an inverse process of the process which is performed by theDPCM encoding section 22 so as to generate the decoded pixel valuesDXV_(p×(r−1)+2) to DXV_(p×r) from the received pixel valueXV_(p×(r−1)+1) and the decompressed differential data DDD_(p×(r−1)+2) toDDD_(p×r), and sequentially outputs the decoded pixel values to theimage data reproduction section 8.

More specifically, the delay section 721 in the DPCM decoding section 72receives the pixel value XV_(p×(r−1)+1) from the packet deassemblingsection 6. The delay section 721 applies a delay amount DL₂ to thereceived pixel value XV_(p×(r−1)+1), and outputs the resultant pixelvalue to the adder section 722 as a delayed pixel value LXV_(p×(r−1)+1).Herein, the delay amount DL₂ is typically an amount of timecorresponding to predetermined clocks. More specifically, the delayamount DL₂ is prescribed to a value which ensures that the decompresseddifferential data DDD_(p×(r−1)+2) from the near-instantaneousdecompression section 71 and the delayed pixel value LXV_(p×(r−1)+1) arereceived by the adder section 722 in the DPCM decoding section 72substantially simultaneously.

The adder section 722 also sequentially receives sets of decompresseddifferential data DDD_(p×(r−1)+2) to DDD_(p×r). The adder section 722adds the decompressed differential data DDD_(p×(r−1)+2) (which isreceived before any other decompressed differential data) and theconcurrently-received delayed pixel value LXV_(p×(r−1)+1) to generate adecoded pixel value DXV_(p×(r−1)+2). The decoded pixel valueDXV_(p×(r−1)+2) which has been thus generated is outputted to the imagedata reproduction section 8 as mentioned above, and is also fed back tothe adder section 722. Next, the adder section 722 adds the decompresseddifferential data DDD_(p×(r−1)+3) from the near-instantaneousdecompression section 71 and the concurrently-received decoded pixelvalue DXV_(p×(r−1)+2) to generate a decoded pixel value DXV_(p×(r−1)+3).The decoded pixel value DXV_(p×(r−1)+3) which has been thus generated isoutputted to the image data reproduction section 8, and also fed back tothe adder section 722. Thereafter, in a repetition of similarprocessing, the adder section 722 adds the decompressed differentialdata DDD_(p×(r−1)+4), DDD_(p×(r−1)+5), . . . DDD_(p×r−1) from thenear-instantaneous decompression section 71 and the previously-generateddecoded pixel values DXV_(p×(r−1)+3), DXV_(p×(r−1)+4), . . . DXV_(p×r−2)to generate decoded pixel values DXV_(p×(r−1)+4), DXV_(p×(r−1)+5), . . .DXV_(p×r−1), respectively, which are outputted to the image datareproduction section 8 and itself. Furthermore, the adder section 722adds the decompressed differential data DDD_(p×r) from thenear-instantaneous decompression section 71 and the previously-generateddecoded pixel value DXV_(p×r−1) to generate a decoded pixel valueDXV_(p×r), which is outputted only to the image data reproductionsection 8. Thus, the DPCM decoding section 72 generates the decodedpixel values DXV_(p×(r−1)+2) to DXV_(p×r), and outputs these decodedpixel values to the image data reproduction section 8.

As a result of the above-described processing, the image datareproduction section 8 sequentially receives q sets of decoded pixelvalues DXV_(p×(r−1)+2) to DXV_(p×r). Furthermore, prior to the arrivalof each set of decoded pixel values DXV_(p×(r−1)+2) to DXV_(p×r), thepixel value XV_(p×(r−1)+1) is received from the packet deassemblingsection 6. In summary, the image data reproduction section 8 firstreceives the pixel value XV₁ and the decoded pixel values DXV₂ toDXV_(p). The pixel value XV₁ and the decoded pixel values DXV₂ toDXV_(p) which are thus generated are substantially identical to thepixel value XV₁ and the pixel values XV₂ to XV_(p) in the first line(along the width direction HD) of the image MG (see FIG. 2A or 2B).Subsequently, as the image data reproduction section 8 receives theq^(th) set of decoded pixel values, all of the pixel valueXV_(p×(r−1)+1) and the decoded pixel values DXV_(p×(r−1)+2) to DXV_(p×r)which are necessary for the reproduction of the image MG are on hand.Thus, as shown in FIG. 20, the image data reproduction section 8generates reproduced image data RTD, which represents an image whichhardly presents any difference to the human eye from the image MDrepresented by the image data TD shown in FIG. 3, by arranging the pixelvalue XV_(p×(r−1)+1) and the decoded pixel values DXV_(p×(r−1)+2) toDXV_(p×r) in the order in which they are received.

As described above, according to the present embodiment of theinvention, encoding and compression are performed for a fixed-lengthdata block DB_(r) which is composed of p pixel values XV_(p×(r−1)+1) toXV_(p×r) arranged in line along the width direction HD. In other words,unlike in the conventional image compression schemes (MPEG or DVC) whereimage correlation on a macro block-by-macro block basis is utilized, thecorrelation between pixels arranged in line along the width direction HDis utilized to compress an image MG. As a result, the delay time whichis incurred before the reproduced image data RTD is generated by thereceiver Rx can be reduced.

In the above embodiment of the invention, the blocking section 1 isillustrated as generating data blocks DB_(r) each composed of p receivedpixel values XV₁ to XV_(i×j), where p is a divisor of i. However, i doesnot need to be an exact integer multiple of p, but any number a of pixelvalues XV may be left as a remainder. In such cases, as shown in FIG.21, the blocking section 1 adds a padding bit sequence PBS composed ofn×(p−a) bits after the a pixel values XV to generate padded data blocksPDB having the same size as that of the respective data blocks DB_(r).Also in the case where i×j is not an exact integer multiple of p, it ispreferable to generate similar padded data blocks PDB.

Based on the above consideration, the data compression section 2 cansubject the padded data blocks to the same processing as that for thedata blocks to generate compressed blocks. Furthermore, since theblocking section 1 only needs to add a padding bit sequence PBS for thepixel values XV arranged in line along the width direction HD, and thereis no need to add any bit sequence along the longitudinal direction VD,the total number of extra bits to be added to the compressed data CD_(r)is much smaller than that required for a typical conventional imagecompression scheme such as the MPEG scheme.

Next, a variant of the above-described data compression section 2 a willbe described with reference to FIGS. 22 and 23. In the followingdescription, the variant of the data compression section 2 a will bereferred to as a “data compression section 2 b”. As shown in FIG. 22,the data compression section 2 b differs from the data compressionsection 2 a in that a DPCM encoding section 25 is employed instead ofthe DPCM encoding section 22. This difference is underlined by the factthat the DPCM encoding section 25 receives compressed differential dataCDD_(p×(r−1)+1) to CDD_(p×r) and a level value LV_(y) from anear-instantaneous compression section 23. Since the data compressionsection 2 b is otherwise identical to the data compression section 2 a,any component elements in the data compression section 2 b which findtheir counterparts in the data compression section 2 a are denoted bythe same reference numerals as those employed in connection with thedata compression section 2 a, and the descriptions thereof are omitted.

As shown in FIG. 23, the DPCM encoding section 25 differs from the DPCMencoding section 22 in that the DPCM encoding section 25 additionallyincludes the near-instantaneous decompression section 251 and the addersection 252, and that the delay section 252 is employed instead of thedelay section 221. Since the DPCM encoding section 25 is otherwiseidentical to the DPCM encoding section 22, any component elements in theDPCM encoding section 25 which find their counterparts in the DPCMencoding section 22 are denoted by the same reference numerals as thoseemployed in connection with the DPCM encoding section 22, and thedescriptions thereof are omitted.

In the DPCM encoding section 25, the near-instantaneous decompressionsection 251 receives the level value LV_(y) from the level determinationsection 232 and the compressed differential data CDD_(p×(r−1)+2) toCDD_(p×r) from the data reduction section 233. By performing anear-instantaneous decompression similar to that performed by thenear-instantaneous decompression section 71 shown in FIG. 16, thenear-instantaneous decompression section 251 generates decompresseddifferential data DDD_(p×(r−1)+2) to DDD_(p×r) from the receivedcompressed differential data CDD_(p×(r−1)+2) to CDD_(p×r) in accordancewith the level value LV_(y), and outputs the decompressed differentialdata DDD_(p×(r−1)+2) to DDD_(p×r) to the adder section 252.

The delay section 253 sequentially receives the pixel valuesXV_(p×(r−1)+1) to XV_(p×r−1), as does the aforementioned delay section221. The delay section 253 applies a delay amount DL₃ to each of thereceived pixel values XV_(p×(r−1)+1) to XV_(p×r−1) to generate delayedpixel values LXV_(p×(r−1)+1) to LXV_(p×r−1), which are outputted to theadder section 252. The delay amount DL₃ is prescribed to a value whichensures that the delayed pixel value LXV_(p×(r−1)×2) from the delaysection 253 and the decompressed differential data DDD_(p×(r−1)+2) fromthe near-instantaneous decompression section 251 are received by theadder section 252 substantially simultaneously. Generally speaking, thedelay amount DL₃ is prescribed to a value which ensures that the delayedpixel values LXV_(p×(r−1)+2), LXV_(p×(r−1)+3), . . . LXV_(p×r−1) and thecompressed differential data CDD_(p×(r−1)+2), CDD_(p×(r−1)+3), . . .CDD_(p×r−1) (which are generated on the basis of the same pixel valuesXV_(p×(r−1)+2), XV_(p×(r−1)+3), . . . XV_(p×r−1), respectively) arereceived by the adder section 252 substantially simultaneously.

The adder section 252 adds the delayed pixel values LXV_(p×(r−1)+2),LXV_(p×(r−1)+3), . . . LXV_(p×r−1) and the concurrently-receivedcompressed differential data CDD_(p×(r−1)+2), CDD_(p×(r−1)+3), . . .CDD_(p×r−1) to generate added pixel values AXV_(p×(r−1)+2),AXV_(p×(r−1)+3), . . . AXV_(p×r−1), which is outputted to thesubtraction section 222. Note that, when the delayed pixel valueLXV_(p×(r−1)+1) from the delay section 253 is received by the addersection 252, the adder section 252 is receiving no input from thenear-instantaneous decompression section 251, so that the adder section252 passes the received delayed pixel value LXV_(p×(r−1)+1) through tothe subtraction section 222 as the added pixel value AXV_(p×(r−1)+1).

As described earlier, the subtraction section 222 receives the pixelvalues XV_(p×(r−1)+2) to XV_(p×r) from the splitter section 21, and theadded pixel values AXV_(p×(r−1)+1) to AXV_(p×r−1) from the adder section252. First, the subtraction section 222 subtracts the added pixel valueAXV_(p×(r−1)+1) from the currently-received pixel value XV_(p×(r−1)+2),and generates a differential data DD_(p×(r−1)+2) representing adifference value therebetween, such that the generated differential dataDD_(p×(r−1)+2) is in the same format as that shown in FIG. 8.Furthermore, the subtraction section 222 subtracts the added pixel valueAXV_(p×(r−1)+2) from the concurrently-received pixel valueXV_(p×(r−1)+3) to generate a differential data DD_(p×(r−1)+3).Thereafter, the subtraction section 222 repeats similar processes untilit generates the aforementioned differential data DD_(p×r). As shown inFIG. 23, the subtraction section 222 sequentially outputs the generateddifferential data DD_(p×(r−1)+2) to DD_(p×r) to the near-instantaneouscompression section 23.

For various reasons such as transmission errors, it might be possiblefor the receiver Rxa to miss, i.e., fail to correctly receive, all ofthe data packet DP_(r) which have been sent from the transmitter Tx.Next, with reference to FIG. 24, a variant of the receiver Rxa which cansolve the above problem will be described. In the following description,the variant of the receiver Rxa will be referred to as a “receiver Rxb”.As shown in FIG. 24, the receiver Rxb differs from the receiver Rxa inthat the receiver Rxb includes a missing block recovery section 9immediately before the image data reproduction section 8. Since thereceiver Rxb is otherwise identical to the receiver Rxa, any componentelements in the receiver Rxb which find their counterparts in thereceiver Rxa are denoted by the same reference numerals as thoseemployed in connection with the receiver Rxa, and the descriptionsthereof are omitted.

The missing block recovery section 9 receives q sets of decoded pixelvalues DXV_(p×(r−1)+2) to DXV_(p×r) from the decompression/decodingsection 7. Prior to the arrival of each set of decoded pixel valuesDXV_(p×(r−1)+2) to DXV_(p×r), the missing block recovery section 9receives the pixel value XV_(p×(r−1)+1) from the packet deassemblingsection 6. Thus, granted that there is no transmission error or thelike, the missing block recovery section 9 will first receive the pixelvalue XV₁ and the decoded pixel values DXV₂ to DXV_(p). Subsequently, asthe missing block recovery section 9 receives the q^(th) set of decodedpixel values, all of the pixel value XV_(p×(r−1)+1) and the decodedpixel values DXV_(p×(r−1)+2) to DXV_(p×r) which are necessary for thereproduction of the image MG are on hand. Thus, when the pixel valueXV_(p×(r−1)+1) and the set of decoded pixel values DXV_(p×(r−1)+2) toDXV_(p×r), which together compose one frame, are all correctly received,the missing block recovery section 9 sequentially outputs these valuesto the image data reproduction section 8.

However, due to the aforementioned transmission error or the like, thereceiver Rxb may miss or fail to receive the pixel value XV_(p×(r−1)+1)and the decoded pixel values DXV_(p×(r−1)+2) to DXV_(p×r) to begenerated from one or more data packets DP_(r). In the followingdescription, any data packets DP_(r) which the receiver Rxb fails toreceive will be referred to as “missing data packets DDP_(r)”. In suchcases, the missing block recovery section 9 is able to virtuallyreproduce the pixel values XV_(p×(r−1)+1) to DXV_(p×r) which have beencontained in the missing data packet DDP_(r) from thecorrectly-generated set of the pixel value XV_(p×(r−1)+1) and thedecoded pixel values DXV_(p×(r−1)+2) to DXV_(p×r).

For example, as shown in FIG. 25, it is assumed that a data packetDP_(r1) which is generated as an r₁ ^(th) data packet in the transmitterTx happens to become a missing data packet DDP_(r1), and that thereceiver Rxb is correctly receiving all the other data packets DP_(r).In this exemplary case, the missing block recovery section 9 firstselects the pixel value XV_(p×((r1−i/p)−1)+1) and the decoded pixelvalues DXV_(p×((r1−i/p)−1)+2) to DXV_(p×(r1−i/p)) which have beengenerated from a data packet DP_(r1−i/p) which lies (i/p) data packetsbefore the missing data packet DP_(r1). Note that the pixel valueXV_(p×((r1−i/p)−1)+1) and the decoded pixel valuesDXV_(p×((r1−i/p)−1)+2) to DXV_(p×(r1−i/p)) are located one line above(along the longitudinal direction VD) the pixel value XV_(p×(r1−1)+1)and the decoded pixel values DXV_(p×(r1−1)+2) to DXV_(p×r1) which wouldhave been generated from the missing data packet DP_(r1). Furthermore,the missing block recovery section 9 selects the pixel valueXV_(p×((r1+i/p)−1)+1) and the decoded pixel valuesDXV_(p×((r1+i/p)−1)+2) to DXV_(p×(r1+i/p)) which have been generatedfrom a data packet DP_(r1+i/p) which lies (i/p) after the missing datapacket DP_(r1). Note that the pixel value XV_(p×((r1+i/p)−1)+1) and thedecoded pixel values DXV_(p×((r1+i/p)−1)+2) to DXV_(p×(r1+i/p)) arelocated one line below (along the longitudinal direction VD) the pixelvalue XV_(p×(r1−1)+1) and the decoded pixel values DXV_(p×(r1−1)+2) toDXV_(p×r1) which would have been generated from the missing data packetDP_(r1).

Next, the missing block recovery section 9 assigns an average valueAV_(p×(r1−1)+1) of the pixel value XV_(p×((r1−i/p)−1)+1) and theXV_(p×((r1+i/p)−1)+1) as the pixel value XV_(p×(r1−1)+1). Moreover, themissing block recovery section 9 assigns an average valueAV_(p×(r1−1)+2) of the decoded pixel value DXV_(p×((r1−i/p)−1)+2) andDXV_(p×((r1+i/p)−1)+2) as the decoded pixel value XV_(p×(r1−1)+2).Thereafter, similar average values AV_(p×(r1−1)+3) to AV_(p×r1) areassigned as the decoded pixel values DXV_(p×(r1−1)+2) to DXV_(p×r1).Instead of the pixel value XV_(p×(r−1)+1) and the decoded pixel valuesDXV_(p×(r−1)+2) to DXV_(p×r) which were never obtained, the missingblock recovery section 9 outputs the average values AV_(p×(r1−1)+1) toAV_(p×r1) which have virtually been reproduced in the above manner tothe image data reproduction section 9. Based on the above-describedaverage values AV_(p×(r1−1)+1) to AV_(p×r1) as well as the pixel valueXV_(p×(r−1)+1) and the decoded pixel values DXV_(p×(r−1)+2) to DXV_(p×r)which have been generated from all the data packets DP_(r) except forthe missing data packet DDP_(r1), the image data reproduction section 9generates reproduced image data RTD₂ which is similar to theaforementioned reproduced image data RTD₁.

The reproduced image data RTD₂ and the aforementioned reproduced imagedata RTD₁ are substantially identical (i.e., indistinguishable to thehuman eye) for the following reasons. The transmitter Tx performs DPCMencoding and near-instantaneous compression on the basis of the datablocks DB_(r), so that the missing data packet DDP_(r) does not exertany influence on the near-instantaneous decompression and DPCM decodingperformed for the other data packets DP_(r). Furthermore, each datablock DB_(r) only includes p pixel values XV_(p×(r−1)+1) to DXV_(p×r).Therefore, the reproduced image data RTD₂ containing the aforementionedaverage value AV_(p×(r1−1)+1) to AV_(p×r1) would hardly present anydifference to the human eye from the reproduced image data RTD₁.

As can be seen from the above, in accordance with the receiver Rxb, anymissing data packets DDP_(r) can be approximately recovered based on theother data packets DP_(r), thereby solving the aforementioned problemand generating reproduced image data RTD₂ which is visually acceptable.

Alternatively, the missing block recovery section 9 may utilize, inorder to deal with the missing data packet DDP_(r), the pixel valueXV_(p×(r−1)+1) and a set of decoded pixel values DXV_(p×(r−1)+2) toDXV_(p×r) from one line above or below (along the longitudinal directionVD) the missing data packet DDP_(r). Further alternatively, the missingblock recovery section 9 may utilize the pixel value XV_(p×(r−1)+1) anda set of decoded pixel values DXV_(p×(r−1)+2) to DXV_(p×r) from onepixel value right or left (along the width direction HD) of the missingdata packet DDP_(r). In particular, in the case where moving picturesare represented by the image data TD, the pixel value XV_(p×(r−1)+1) anda set of decoded pixel values DXV_(p×(r−1)+2) to DXV_(p×r) which aregenerated from a data packet DP_(r) pertaining to a preceding and/orsucceeding frame may be employed in the receiver Rxb.

Next, with reference to FIG. 26, a second implementation of the datacompression section 2 shown in FIG. 1 will be described. In thefollowing description, the second implementation of the data compressionsection 2 will be referred to as a “data compression section 2 c”. Inorder to perform the aforementioned second compression process, the datacompression section 2 c includes an orthogonal transform section 26 anda data reduction section 27, as shown in FIG. 26.

Next, the second compression process which is performed by the datacompression section 2 c will be specifically described. Data blocksDB_(r) from the aforementioned blocking section 1 (see FIG. 1) arereceived by an orthogonal transform section 26 in the data compressionsection 2 c. The orthogonal transform section 26 performs an orthogonaltransform to multiply the received set of pixel values XV_(p×(r−1)+1) toXV_(p×r) by a predetermined orthogonal transform matrix, therebygenerating a set of coefficients CF_(p×(r−1)+1) to CF_(p×r). As shown inFIG. 27, these coefficients CF_(p×(r−1)+1) to CF_(p×r) which are derivedthrough the orthogonal transform are expressed in n bits, as are thepixel values XV_(p×(r−1)+1) to XV_(p×r). Furthermore, the coefficientsCF_(p×(r−1)+1) to CF_(p×r) represent respectively different frequencycomponents in the frequency domain. The above set of coefficientsCF_(p×(r−1)+1) to CF_(p×r) are outputted from the orthogonal transformsection 26 to the data reduction section 27.

Hereinafter, an Hadamard transform will be described as an example ofthe aforementioned orthogonal transform, and the process performed bythe orthogonal transform section 26 will be more specifically described.As described earlier, each data block DB_(r) includes p pixel valuesXV_(p×(r−1)+1) to XV_(p×r). In the following description, p isconveniently assumed to be 16. Under this assumption, the orthogonaltransform section 26 retains a (16×16) Hadamard transform matrix H asexpressed by eq. 1 below:

$\begin{matrix}{{{H = \frac{1}{\sqrt{16}}}\quad}\begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} \\1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 & 1 & 1 \\1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} \\1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 \\1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 & 1 & 1 & {- 1} & {- 1} \\1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 \\1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 \\1 & {- 1} & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} \\1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1} & {- 1} & 1 & 1 & {- 1} & 1 & {- 1} & {- 1} & 1 \\1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1} \\1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 & 1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 \\1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & 1 & {- 1} & 1 & {- 1} \\1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 \\1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1} & 1 & {- 1}\end{bmatrix}} & {{eq}.\; 1}\end{matrix}$

For conciseness, the pixel values XV_(16×r−15) to XV_(16×r) contained inthe currently-received data block DB_(r) are represented as a matrixexpressed by eq. 2 below. The coefficients CF_(16×r−15) to CF_(16×r)obtained through the Hadamard transform are represented as a matrixexpressed by eq. 3 below.x=[pixel value XV_(16×r−15), pixel value XV_(16×r−14), . . . , pixelvalue XV_(16×r)]^(t)  eq. 2y=[coefficient CF_(16×r−15), coefficient CF_(16×r−14), . . . ,coefficient CF_(16×r)]^(t)  eq. 3

In eq. 2 and eq. 3, “t” means transpose.

Under the definitions expressed by eq. 1 to eq. 3 above, the orthogonaltransform section 26 multiplies the Hadamard transform matrix H by thematrix “x” beginning from the right side thereof, as expressed by eq. 4below.y=H×x/4  eq. 4

The resultant coefficient CF_(16×r−15) is an integer in the range from 0to 255, and the resultant coefficients CF_(16×r−14) to CF_(16×r) areintegers in the range from −127 to 127. Therefore, these coefficientscan all be expressed in n bits as mentioned above. According to theHadamard transform matrix H expressed by eq. 1 above, the coefficientCF_(16×r−15) represents a component associated with the lowest frequencyregion. Likewise, the coefficients CF_(16×r−15) to CF_(16×r) havinggreater suffix values represent components which are associated withrespectively higher frequency regions.

As described earlier, the data reduction section 27 sequentiallyreceives sets of coefficients CF_(p×(r−1)+1) to CF_(p×r). From eachreceived set of coefficients CF_(p×(r−1)+1) to CF_(p×r), the datareduction section 27 deletes b coefficients CF_(p×r−b) to CF_(p×r) whichrepresent components associated with predetermined high-frequencyregions, thereby generating compressed coefficients CF_(p×(r−1)+1) toCCF_(p×r−(b−1)). Herein, “b” is a natural number in the range from 1 ton.

According to the present embodiment of the invention, as shown in FIG.28, those of the coefficients CF_(p×(r−1)+1) to CF_(p×r) which are to bedeleted are predetermined. FIG. 28 shows example coefficients CF whichare to be deleted in an exemplary case where n=8 and p=16. In principle,among the currently-received coefficients CF_(16×r−15) to CF_(16×r), thedata reduction section 27 leaves intact those which representpredetermined low-frequency components, while deleting those whichrepresent any higher frequency components. In the exemplary case shownin FIG. 28, the coefficients CF_(16×r−15) to CF_(16×r−12), whichrepresent relatively low-frequency components, are left intact (see thehatched portions). On the other hand, the coefficients CF_(16×r−7) toCF_(16×r) representing relatively high frequency components are deleted.The reason why all of the coefficients CF_(16×r−7) to CF_(16×r)representing relatively high-frequency components can be deleted is asfollows. In a set of coefficients (i.e., matrix y (as represented by eq.3)) which are produced through the aforementioned orthogonal transform,the greater coefficients are generally concentrated in the low frequencyregions, whereas the smaller coefficients are generally concentrated inthe high frequency regions, due to certain correlations residing in theimage MG.

According to the present embodiment of the invention, the next bit tothe MSB and the least significant bit (hereinafter referred to as “LSB”)are deleted from both coefficients CF_(16×r−11) and CF_(16×r−10).Furthermore, the next bit to the MSB and the lower two bits are deletedfrom both coefficients CF_(16×r−9) and CF_(16×r−8). More specifically,as shown in FIG. 29, the LSBs in the coefficients CF_(16×r−11) toCF_(16×r−8) are all deleted. If any of the coefficients CF_(16×r−11) toCF CF_(16×r−8) has a positive value and the next bit to the MSB that isto be deleted is “1”, then the other bits are all set to “1”, so theresultant compressed coefficient CCF_(16×r−11) to CCF_(16×r−8) will be abit sequence composed only of “1”. If any of the coefficientsCF_(16×r−11) to CF_(16×r−8) has a positive value and the next bit to theMSB that is to be deleted is “0”, then all the other bits are leftintact. If any of the coefficients CF_(16×r−11) to CF_(16×r−8) has anegative value and the next bit to the MSB that is to be deleted is “1”,then all the other bits are set to “0”. If any of the coefficientsCF_(16×r−11) to CF_(16×r−8) has a negative value and the next bit to theMSB that is to be deleted is “0”, then all the other bits are leftintact.

The present embodiment is not limited to the exemplary cases shown inFIGS. 28 and FIG. 29. It is possible to determine which one of thecoefficients CF_(p×(r−1)+1) to CF_(p×r) are to be deleted and whichbit(s) thereof is to be deleted in accordance with the band width of thetransmission path N, the image quality which is required on the receiverRx side, and the like.

In the above-described manner, the data reduction section 27 generates aset of compressed coefficients CCF_(p×(r−1)+1) to CCF_(p×r−(b−1)), whichare outputted to the data sending section 3 as the aforementionedcompressed block CB_(r).

As shown in FIG. 1, the data sending section 3 includes the buffersection 31 and the sending control section 32. The buffer section 31stores the set of compressed coefficients CCF_(p×(r−1)+1) toCCF_(p×r−(b−1)) as a fixed-length compressed block CB_(r). As in thefirst implementation, since the set of compressed coefficientsCCF_(p×(r−1)+1) to CCF_(p×r−(b−1)) is of a fixed length, any delay timeincurred will be minimized. The sending control section 32 receives theset of compressed coefficients CCF_(p×(r−1)+1) to CCF_(p×r−(b−1)) fromthe buffer section 31, and sends these onto the transmission path N. Asshown in FIG. 1, the set of compressed coefficients CCF_(p×(r−1)+1) toCCF_(p×r−(b−1)), as an example compressed block CB_(r), are transmittedvia the transmission path N so as to be received by the receiver RX.

The receiver Rx subjects the received data packet DP_(r) topredetermined processing to reproduce the image data TD. Hereinafter, asecond implementation of the receiver Rx of FIG. 1 will be describedwith reference to FIG. 30. In the following description, the secondimplementation of the receiver Rx will be referred to as a “receiverRxc”. The receiver Rxc differs from the above-described receiver Rxa(see FIG. 15) in that the receiver Rxc includes a bit decoding section10 and an inverse orthogonal transform section 11 instead of the packetdeassembling section 6 and the decompression/decoding section 7. Sincethe receiver Rxc is otherwise identical to the receiver Rxa, anycomponent elements in FIG. 30 which find their counterparts in FIG. 15are denoted by the same reference numerals as those employed inconnection with the receiver Rxa, and the descriptions thereof areomitted.

Next, the reproduction processing for the image data TD which isperformed by the receiver Rxc having the aforementioned structure willbe described in detail. In the data receiving section 5, the buffersection 51 stores a set of compressed coefficients CCF_(p×(r−1)+1) toCCF_(p×r−(b−1)) from the transmission path N. The buffer section 51,which is only required to store the set of fixed-length compressedcoefficients CCF_(p×(r−1)+1) to CCF_(p×r−(b−1)), as is the case with thebuffer section 31, contributes to the minimization of the delay time.After the buffering, the compressed coefficients CCF_(p×(r−1)+1) toCCF_(p×r−(b−1)) are outputted to the bit decoding section 10 via thereception control section 52.

The bit decoding section 10 performs an inverse process of the processwhich is performed by the data reduction section 27 so as to generatethe decompressed coefficients DCF_(p×(r×1)+1) to DCF_(p×r) from thecompressed coefficients CCF_(p×(r−1)+1) to CCF_(p×r−(b−1)), which arethen outputted to the inverse orthogonal transform section 11. Herein,the decompressed coefficients DCF_(p×(r−1)+1) to DCF_(p×r) have suchsmall differences from the coefficients CF_(p×(r−1)+1) to CF_(p×r) thatthe decoded pixel values DXV_(p×(r−1)+1) to DXV_(p×r) (described later)and the pixel values XV_(p×(r−1)+1) to XV_(p×r) would hardly present anydifference to the human eye. To describe the bit restoration processmore specifically, an average value of a bit sequence of 1 and/or 0,i.e., values which can be expressed in two bits, is added after the LSBof each of the compressed coefficients CCF_(16×r−9) and CCF_(16×r−8).Furthermore, in the case where the MSB in the compressed coefficientCCF_(16×r−9) and/or CCF_(16×r−8) has a positive value, “0” is insertedafter the MSB of that compressed coefficient; otherwise, “1” is insertedafter the MSB of that compressed coefficient. Thus, the decompressedcoefficients DCF_(16×r−9) and DCF_(16×r−8) are generated. Moreover, abit “1” or “0” is added after the LSB of each of the compressedcoefficients CCF_(16×r−11) and CCF_(16×r−10). Furthermore, in the casewhere the MSB in the compressed coefficient CCF_(16×r−11) and/orCCF_(16×r−10) has a positive value, “0” is inserted after the MSB ofthat compressed coefficient; otherwise, “1” is inserted after the MSB ofthat compressed coefficient. Thus, the decompressed coefficientsDCF_(16×r−11) and DCF_(16×r−10) are generated. In order to deal with thecoefficients CF_(16×r−7) and DCF_(16×r) from which all bits have beendeleted, the bit decoding section 10 generates decompressed coefficientsDCF_(16×r−7) and DCF_(16×r) whose eight bits are all “0”.

The inverse orthogonal transform section 11 performs an inverseorthogonal transform, i.e., an inverse process of the process which isperformed by the orthogonal transform section 26, to multiply an inversematrix of the aforementioned orthogonal transform matrix by the receiveddecompressed coefficients DCF_(p×(r−1)+1) to DCF_(p×r), therebygenerating a set of decoded pixel values DXV_(p×(r−1)+1) to DXV_(p×r).The resultant decoded pixel values DXV_(p×(r−1)+)to DXV_(p×r), whichhardly present any difference to the human eye as compared to the pixelvalues XV_(p×(r−l)+1) to XV_(p×r), are outputted to the image datareproduction section 8.

As described earlier, the present embodiment of the invention isdirected to the case where an Hadamard transform is performed. Next, theprocessing to be performed by the inverse orthogonal transform section11 in this specific case will be described more specifically. Thefollowing description also assumes that p=16. Under this assumption, theinverse orthogonal transform section 11 retains an inverse transformmatrix H⁻¹ of eq. 1 above. For conciseness, the currently-receiveddecompressed coefficients DCF_(p×(r−1)+1) to DCF_(p×r) are representedas a matrix expressed by eq. 5 below. The decoded pixel valuesDXV_(p×(r−1)+1) to DXV_(p×r) which are obtained through the inversetransform of the Hadamard transform are represented as a matrixexpressed by eq. 6 below.y=[decompressed coefficient CF_(16×r−15), . . . , decompressedcoefficient CF_(16×r)]^(t)  eq. 5z=[decoded pixel value XV_(16×r−15), . . . , decoded pixel valueXV_(16×r)]^(t)  eq. 6In eq. 5 and eq. 6, “t” means transpose.

Under the definitions expressed by eq. 5 and eq. 6 above, the inverseorthogonal transform section 11 multiplies the matrix “y” by the inversetransform matrix H⁻¹ of the Hadamard transform matrix H beginning fromthe right side thereof, as expressed by eq. 7 below.z=H ⁻¹ ×y×4  eq. 7

As a result of the above processing, the image data reproduction section8 sequentially receives q sets of decoded pixel values DXV_(p×(r−1)+1)to DXV_(p×r). The image data reproduction section 8 generates areproduced image data RTD similar to that shown in FIG. 20.

As described above, in accordance with the second implementation of thedata compression section 2 c, too, encoding and compression areperformed for the fixed-length data block DB_(r) composed of p pixelvalues XV_(p×(r−1)+1) to XV_(p×r) arranged in line along the widthdirection HD, it is possible to minimize any delay time elapsing priorto the generation of the reproduced image data RTD in the receiver Rxc.

Although the above illustration is directed to the case where anHadamard transform is performed in the orthogonal transform section 26,the present invention is not limited thereto. Alternatively, theorthogonal transform section 26 may perform a DCT or discrete sinetransform (DST).

“First Application”

In recent years, there has been plenty of work directed to the researchand development of driving assistant systems for assisting a driver inhis/her driving of a vehicle by capturing an image of the surroundingsof the vehicle via image capturing devices and providing such an imageto the driver. Next, a driving assistant system TS₁ incorporating theabove-described transmitter Tx and receiver Rx will be described. FIG.31 is a block diagram illustrating the overall configuration of thedriving assistant system TS₁. The driving assistant system TS₁ shown inFIG. 31 includes two image capturing devices 13, two image processingsections 14, two transmitters Tx, a transmission path N, a receiver Rx,an image synthesis section 15, and a display section 16. The drivingassistant system TS₁ is mounted in a vehicle V_(ur).

The image capturing devices 13, each of which is disposed so as to beable to capture an image of an area in the rear of the vehicle V_(ur),capture images of respectively different regions in the rear of thevehicle V_(ur), and generate captured image data CTD representing thecaptured images MG (see FIG. 32). After each image capturing device 13,an implementation of the aforementioned image processing section 14 iscoupled so as to receive the respective captured image data CTD fromthat image capturing device 13.

As shown in FIG. 32, from the received image data CTD, each imageprocessing section 14 selects a number of pixels composing a partialimage PMG representing a predetermined portion of the image indicativeof the surroundings of the vehicle, thereby generating a partial imagedata PTD (this process being referred to as “clipping”). Herein, it isconveniently assumed that each partial image data PTD is of the formatshown in FIG. 3 in the present embodiment of the invention. After eachimage processing section 14, an implementation of the aforementionedtransmitter Tx is coupled so as to receive the respective image data PTDfrom that image processing section 14.

Each transmitter Tx performs the processing described in any of theearlier embodiments of the invention for the partial image data PTD itreceives, thereby generating compressed block CB_(r). The respectivecompressed blocks CB_(r) are transmitted to the receiver Rx via thetransmission path N.

The receiver Rx performs the processing described in any of the earlierembodiments of the invention for each received compressed block CB_(r),thereby generating reproduced partial image data RPTD. Herein, as willbe appreciated from the foregoing description, each reproduced partialdata RPTD represents a reproduced partial image RMG which issubstantially the same as the image MG represented by each partial imagedata PTD (as shown in FIG. 32). The respective reproduced partial dataRPTD are outputted to the subsequent image synthesis section 15.

The image synthesis section 15 performs a synthesis process for bothreceived reproduced partial image data RPTD to generate a merged imagedata MTD representing a single synthesized image MMG which is composedof the two partial images PMG. The merged image data MTD is outputted tothe display section 16.

The display section 16 subjects the received merged image data MTD todisplay processing, thereby providing the aforementioned synthesizedimage MMG to the driver of the vehicle V_(ur).

Thus, in accordance with the present driving assistant system TS₁, eachimage processing section 14 generates a partial image data PTD which isrequired on the receiver Rx side, so that the amount of data which istransmitted over the transmission path N can be minimized.

Moreover, in accordance with the transmitters Tx and the receiver Rx, asdescribed earlier, the delay time which is incurred after the generationof captured image data CTD by the image capturing devices 13 and beforethe display processing of the merged image data MTD by the displaysection 16 can be minimized. By incorporating the transmitters Tx andthe receiver Rx having such characteristics in the driving assistantsystem TS₁, a driver is enabled to grasp the surroundings of the vehicleV_(ur) in real time. As a result, the driver can drive the vehicleV_(ur) with increased safety.

Next, with reference to FIG. 33, the above-described technologicaleffects will be more specifically described. In FIG. 33, the vehicleV_(ur) is moving “in reverse” (i.e., backing up) in a direction shown byarrow A₁. An obstacle BST is present at a distance from the vehicleV_(ur) in the direction (indicated by arrow A₁) in which the vehicleV_(ur) is moving. The driver will try to drive the vehicle V_(ur) so asnot to collide with the obstacle BST by checking the synthesized imageMTD which is displayed on the display section 16. In FIG. 33, a point P₀is a position where the rear end of the vehicle V_(ur) passes at thecurrent time T₀. Given that the aforementioned delay time is DT, thesynthesized image MTD which is displayed on the display section 16 atthe current time T₀ is an image generated based on the captured imagedata CTD which was generated by the image capturing devices 13 at a time(T₀−t).

In FIG. 33, a point P₁ is a position where the rear end of the vehicleV_(ur) passed at the aforementioned time (T₀−t), i.e., where thecaptured image data CTD was generated. Herein, the distance Δd betweenthe points P₀ and P₁ is determined by the velocity SP of the vehicleV_(ur) and the delay time DT, as expressed by eq. 8 below.Δd=SP×DT  eq. 8

Assuming that the vehicle V_(ur) moves at a constant velocity, as seenfrom eq. 8 above, the distance Δd increases as the delay time DTincreases. If the delay time DT=0, then the distance Δd=0, so that thepoints P₀ and P₁ will coincide. If there is substantial delay time DT,on the other hand, the vehicle V_(ur) may collide into the obstacle BSTbefore the display section 16 displays the sight of the collision invain. From this perspective, it can be seen how useful it is toincorporate transmitters Tx and a receiver Rx having a sufficientlysmall delay time DT in the driving assistant system TS₁.

In the above application, the driving assistant system TS₁ comprises twosets of image capturing devices 13, image processing sections 14, andimage transmitters Tx. However, the present invention is not limited tosuch a configuration. The driving assistant system TS₁ may comprise oneor more set of such elements. Although the above image capturing devices13 are illustrated as being capable of capturing images of objects atthe rear of the vehicle V_(ur), the image capturing devices 13 mayalternatively be fixed on the vehicle V_(ur) so as to be capable ofcapturing images of objects at the front and/or sides of the vehicleV_(ur), as necessary.

While the missing block recovery section 9 in the earlier-describedembodiment is illustrated as approximately recovering the pixel valuesXV_(p×(r−1)+1) to DXV_(p×r) which have been contained in a missing datapacket DDP_(r) from a correctly-generated set of the pixel valueXV_(p×(r−1)+1) and the decoded pixel values DXV_(p×(r−1 )+2) toDXV_(p×r), it may be more preferable in the driving assistant system TS₁not to reproduce any missing data packets DDP_(r), but simply “blackout” that portion, for example, thereby warning the driver of theoccurrence of the missing data packets DDP_(r), because the driver is inneed of accurate information concerning the surroundings of the vehicleV_(ur).

“Second Application”

In the field of FA (Factory Automation), there has been some researchand development work on remote control systems for acting on an objectvia remote control. Next, a remote control system TS₂ incorporating theabove-described transmitter Tx and the receiver Rx will be described.FIG. 34 is a block diagram illustrating the overall structure of theremote control system TS₂. The remote control system TS₂ of FIG. 34includes an image capturing device 17, a transmitter Tx, a transmissionpath N, a receiver Rx, a display section 18, a control section 19, acontrol data generation section 110, a control data sending section 111,a control data receiving section 112, and a manipulator section 113. Theremote control system TS₂ is employed to exert an action on an objectTG.

The image capturing device 17, which is disposed in the neighborhood ofthe object TG, captures an image of the object TG, and generatescaptured image data CTD representing the captured image. The generatedcaptured image data CTD is outputted to the transmitter Tx. Thetransmitter Tx subjects the received captured image data CTD to theprocessing which has been described in any of the foregoing embodimentsof the invention, thereby generating compressed block CB_(r) asdescribed above. The compressed block CB_(r) is transmitted to thereceiver Rx via the transmission path N.

The receiver Rx subjects the received compressed block CB_(r) to theprocessing which has been described in the foregoing embodiment of theinvention, thereby generating reproduced image data RTD. Herein, as willbe appreciated from the foregoing description, the reproduced image dataRTD represents an image of the object TG which is substantially the sameas the image represented by the captured image data CTD. The reproducedimage data RTD is outputted to the display section 18. The displaysection 18 subjects the received reproduced image data RTD to displayprocessing, thereby providing an image representing the object TG to anoperator.

While checking on the display section 18, the operator operates thecontrol section 19 to instruct as to what sort of action to exert on theobject TG. In response to the instruction from the control section 19,the control data generation section 110 generates control data CTLDrepresenting an action to be exerted on the object, which is outputtedto the control data sending section 111. The control data sendingsection 111 sends the received control data CTLD onto the transmissionpath N, which then is transmitted to the control data receiving section112. The manipulator section 113 exerts an action on the object TG inaccordance with the control data CTLD which is received by the controldata receiving section 112.

As described above, in accordance with the transmitter Tx and thereceiver Rx, the delay time which is incurred after the generation ofcaptured image data CTD by the image capturing device 17 and before thedisplay processing by the display section 18 can be minimized. Byincorporating the transmitters Tx and the receiver Rx having suchcharacteristics in the remote control system TS₂, an operator is enabledto grasp the situation concerning the object TG in real time. As aresult, the operator can properly act on the object TG from a remoteplace.

Although the above-described application assumes that the operatoroperates the control section 19 while looking at the display section 18,it is also possible to automatically control the operation of the robot(or the manipulator section 113) by applying image recognitiontechniques.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

1. An image transmitter for compressing image data and transmitting theimage data to a receiver via a transmission path, wherein the image dataat least contains i pixel values of pixels arranged in line along asingle direction, each pixel value being expressed in n bits, the imagetransmitter comprising: a blocking section for taking every p pixelvalues among the i pixel values in the image data to form a data block,and sequentially outputting a plurality of data blocks each including ppixel values; a data compression section for reducing an amount of datafrom each data block outputted from the blocking section to output acompressed block for each data block, the data compression sectioncompressing each data block based on a level value derived from adifferential pulse code modulation result of two adjoining pixel values;and a data sending section for sending each compressed block outputtedfrom the data compression section onto the transmission path, wherein i,n, and p are predetermined natural numbers, and the data compressionsection deletes a bit, among all bits of a data block, from each datablock based on the level value, wherein the data compression sectioncomprises: a DPCM encoding section for performing a differential pulsecode modulation based on two adjoining pixel values in each data blockgenerated by the blocking section to generate and output differentialdata; a near-instantaneous compression section for performing anear-instantaneous compression for the differential data outputted fromthe DPCM encoding section to reduce a number of bits in the differentialdata, and generating and outputting compressed differential data; and apacket assembling section for generating and outputting a data packet tothe data sending section as the compressed block, the data packetcontaining a first pixel value in the data block generated by theblocking section and the respective compressed differential dataoutputted from the near-instantaneous compression section, wherein theDPCM encoding section comprises: a delay section for applying apredetermined delay amount to 1^(st) to (p−1)^(th) pixel values in eachdata block generated by the blocking section, and outputting delayedpixel values; and a subtraction section for calculating respectivedifferences between 2 to p pixel values in each data block generated bythe blocking section and 1^(st) to (p−1)^(th) delayed pixel valuesoutputted from the delay section to generate (p−1) differential data asthe differential data, and outputting the (p−1) differential data to thenear-instantaneous compression section, and wherein thenear-instantaneous compression section comprises: a buffer section forstoring the (p−1) differential data outputted from the DPCM encodingsection; a level determination section for generating the level valuebased on each of the (p−1) differential data outputted from the buffersection and outputting the level value, the level value determining abit to be deleted from each of the (p−1) differential data; and a datareduction section for deleting the bit, as determined by the level valueoutputted from the level determination section, from each differentialdata outputted from the buffer section to generate (p−1) compresseddifferential data as the compressed differential data, and outputtingthe (p−1) compressed differential data to the packet assembling section.2. The image transmitter according to claim 1, wherein: the compressedblock has a fixed length; and the data sending section comprises: abuffer section for storing the compressed block; and a sending controlsection for sending the compressed block stored in the buffer sectiononto the transmission path.
 3. The image transmitter according to claim1, wherein the level determination section comprises: a differentialdata selection section for selecting one of the respective (p−1)differential data outputted from the buffer section which has a greatestabsolute value, and outputting the selected differential data as amaximum differential data; and a level selection section for selectingone of a predetermined number of the level values based on the maximumdifferential data outputted from the differential data selectionsection, and outputting the selected level value to the data reductionsection.
 4. The image transmitter according to claim 3, wherein: thedata reduction section deletes t bits, as determined by the level valueoutputted from the level determination section, from each differentialdata outputted from the buffer section to generate the (p−1) compresseddifferential data; and t is a natural number.
 5. The image transmitteraccording to claim 1, wherein the data packet generated by the packetassembling section contains the first pixel value in each data blockgenerated by the blocking section, the level value outputted from thelevel determination section, and the (p−1) compressed differential dataoutputted from the data reduction section.
 6. The image transmitteraccording to claim 1, wherein, when p pixel values among the i pixelvalues in the image data cannot be taken to form a data block, theblocking section generates a padded data block by using a predeterminedpadding bit, the padded data block having the same size as that of thedata block.
 7. A transmission system including the receiver and theimage transmitter according to claim 1, wherein the receiver comprises:a data receiving section for receiving the data packet transmitted viathe transmission path and outputting the received data packet; a packetdisassembling section for disassembling the data packet outputted fromthe data receiving section into the first pixel value in the data blockand the respective compressed differential data generated by thenear-instantaneous compression section, and outputting the first pixelvalue in the data block and the respective compressed differential data;a near-instantaneous decompression section for restoring the bits havingbeen deleted from the compressed differential data generated by thenear-instantaneous compression section to generate and outputdecompressed differential data; a DPCM decoding section for performingan inverse process of the differential pulse code modulation performedby the DPCM encoding section, generating decoded pixel values from therespective decompressed differential data outputted from thenear-instantaneous decompression section, and outputting the decodedpixel values; and an image data reproduction section for generatingreproduced image data from the first pixel value outputted from thepacket disassembling section and the respective decoded pixel valuesoutputted from the DPCM decoding section, the reproduced image datarepresenting an image.
 8. The transmission system according to claim 7,wherein: the data packet has a fixed length; and the data receivingsection comprises: a buffer section capable of storing at least the datapacket of the fixed length; and a reception control section foroutputting the data packet stored in the buffer section to the packetdisassembling section.
 9. The transmission system according to claim 7,wherein the receiver further comprises: a missing block recovery sectionfor, when a data packet is missed by the data receiving section,reproducing pixel values contained in the missing data packet based on afirst pixel value from at least one other data packet from the packetdisassembling section and decoded pixel values from the at least oneother data packet from the DPCM decoding section, and outputting thepixel values to the image data reproduction section.
 10. A drivingassistant system for assisting in the driving of a vehicle, the drivingassistant system comprising: a transmission path; a plurality of imagecapturing devices each of which is fixed on the vehicle and whichcaptures an image of surroundings of the vehicle and outputs capturedimage data; a plurality of image processing sections each of which isconnected to an image capturing device of the image capturing devicesand performs a clipping process for the captured image data outputtedfrom the respective image capturing device to generate partial imagedata, wherein each partial image data at least contains i pixel valuesof pixels arranged in line along a single direction, each pixel valuebeing expressed in n bits; and a plurality of transmitters each of whichis associated with one of the plurality of image processing sections,wherein each transmitter comprises: a blocking section for taking everyp pixel values among the i pixel values in the partial image data fromthe associated image processing section to form a data block, andsequentially outputting a plurality of data blocks each including ppixel values, a data compression section for reducing an amount of datafrom each data block outputted from the blocking section to output acompressed block for each data block, the data compression sectionreducing the amount of data based on a level value derived from adifferent pulse code modulation result of two adjoining pixel values,and a data sending section for sending each compressed block outputtedfrom the data compression section onto the transmission path; a receiverfor receiving and decompressing each compressed block from thetransmission path, restoring each data block, and reproducing therespective partial image data; an image synthesis section for performinga synthesis process for the partial image data from the receiver andoutputting merged image data, the merged image data representing animage in which images represented by the respective partial image dataare synthesized; and a display section for displaying the imagerepresented by the merged image data outputted from the image synthesissection, wherein i, n, and p are predetermined natural numbers, and thedata compression section deletes a bit, among all bits of a data block,from each data block based on the level value, wherein the datacompression section of each transmitter comprises: a DPCM encodingsection for performing a differential pulse code modulation based on twoadjoining pixel values in each data block generated by the blockingsection to generate and output differential data; a near-instantaneouscompression section for performing a near-instantaneous compression forthe differential data outputted from the DPCM encoding section to reducea number of bits in the differential data, and generating and outputtingcompressed differential data; and a packet assembling section forgenerating and outputting a data packet to the data sending section asthe compressed block, the data packet containing a first pixel value inthe data block generated by the blocking section and the respectivecompressed differential data outputted from the near-instantaneouscompression section, wherein the DPCM encoding section of eachtransmitter comprises: a delay section for applying a predetermineddelay amount to 1^(st) to (p−1)^(th) pixel values in each data blockgenerated by the blocking section, and outputting delayed pixel values;and a subtraction section for calculating respective differences between2^(nd) to p^(th) pixel values in each data block generated by theblocking section and 1^(st) to (p−1)^(th) delayed pixel values outputtedfrom the delay section to generate (p−1) differential data as thedifferential data, and outputting the (p−1) differential data to thenear-instantaneous compression section, and wherein thenear-instantaneous compression section of each transmitter comprises: abuffer section for storing the (p−1) differential data outputted fromthe DPCM encoding section; a level determination section for generatingthe level value based on each of the (p−1) differential data outputtedfrom the buffer section and outputting the level value, the level valuedetermining a bit to be deleted from each of the (p−1) differentialdata; and a data reduction section for deleting the bit, as detenriinedby the level value outputted from the level determination section, fromeach differential data outputted from the buffer section to generate(p−1) compressed differential data as the compressed differential data,and outputting the (p−1) compressed differential data to the packetassembling section.
 11. A remote control system for exerting an actionon an object via remote control, the remote control system comprising: atransmission path; an image capturing device which is provided in aneighborhood of the object and captures an image of surroundings of theobject and outputs captured image data, wherein the captured image dataat least contains i pixel values of pixels arranged in line along asingle direction, each pixel value being expressed in n bits; and atransmitter, wherein the transmitter comprises: a blocking section fortaking every p pixel values among the i pixel values in the capturedimage data from the image capturing device to form a data block, andsequentially outputting a plurality of data blocks each including ppixel values; a data compression section for reducing an amount of datafrom each data block outputted from the blocking section to output acompressed block for each data block, the data compression sectionreducing the amount of data based on a level value derived from adifferential pulse code modulation result of two adjoining pixel values,and a data sending section for sending each compressed block outputtedfrom the data compression section onto the transmission path; a receiverfor receiving and decompressing each compressed block from thetransmission path, restoring each data block, and reproducing thecaptured image data; a display section for displaying the imagerepresented by the captured image data outputted from the receiver forviewing by an operator; a control data generation section for generatingand outputting control data for exerting an action on the object inaccordance with control made by the operator; and a control data sendingsection for sending control data from the control data generationsection onto the transmission path; a control data receiving section forreceiving and outputting the control data from the transmission path;and a manipulator section for exerting the action on the object inaccordance with the control data received from the control datareceiving section, wherein i, n, and p are predetermined naturalnumbers, and the data compression section deletes a bit, among all bitsof a data block, from each data block based on the level value, whereinthe data compression section comprises: a DPCM encoding section forperforming a differential pulse code modtilation based on two adjoiningpixel values in each data block generated by the blocking section togenerate and output differential data; a near-instantaneous compressionsection for performing a near-instantaneous compression for thedifferential data outputted from the DPCM encoding section to reduce anumber of bits in the differential data, and generating and outputtingcompressed differential data; and a packet assembling section forgenerating and outputting a data packet to the data sending section asthe compressed block, the data packet containing a first pixel value inthe data block generated by the blocking section and the respectivecompressed differential data outputted from the near-instantaneouscompression section, wherein the DPCM. encoding section comprises: adelay section for applying a predetermined delay amount 1^(st) to(p−1)^(th) pixel values in each data block generated by the blockingsection, and outputting delayed pixel values; and a subtraction sectionfor calculating respective differences between 2^(nd) to p^(th) pixelvalues in each data block generated by the blocking section and 1^(st)to (p−1)^(th) delayed pixel values outputted from the delay section togenerate (p−1) differential data as the differential data, andoutputting the (p−1) differential data to the near-instantaneouscompression section, and wherein the near-instantaneous compressionsection comprises: a buffer section for storing the (p−1) differentialdata outputted from the DPCM encoding section; a level determinationsection for generating the level value based on each of the (p−1)differential data outputted from the buffer section and outputting thelevel value, the level value determining a bit to be deleted from eachof the (p−1) differential data; and a data reduction section fordeleting the bit, as detennined by the level value outputted from thelevel determination section, from each differential data otitputted fromthe buffer section to generate (p−1) compressed differential data as thecompressed differential data, and outputling the (p−1) compresseddifferential data to the packet assembling section.
 12. An imagecompression and transmission method for compressing image data andtransmitting the image data to a receiver via a transmission path,wherein the image data at least contains i pixel values of pixelsarranged in line along a single direction, each pixel value beingexpressed in n bits, the image compression and transmission methodcomprising: a blocking operation of taking every p pixel values amongthe i pixel values in the image data to form a data block, andsequentially outputting a plurality of data blocks each including ppixel values; a data compression operation of reducing an amount of datafrom each data block outputted in the blocking operation to output acompressed block for each data block based on a level value derived froma differential pulse code modulation result of two adjoining pixelvalues; and sending each compressed block outputted in the datacompression operation onto the transmission path, wherein i, n, and pare predetermined natural numbers, and the data compression operationdeletes a bit, among all bits of a data block, from each data blockbased on the level value, wherein the data compression operationcomprises: a DPCM encoding operation of performing a differential pulsecode modulation based on two adjoining pixel values in each data blockgenerated by the blocking operation to generate and output differentialdata; a near-instantaneous compression operation of performing anear-instantaneous compression for the differential data outputted bythe DPCM encoding operation to reduce a number of bits in thedifferential data, and generating and outputting compressed differentialdata; and a packet assembling operation of generating and outputting adata packet for the sending operation as the compressed block, the datapacket containing a first pixel value in the data block generated by theblocking operation and the respective compressed differential dataoutputted by the near-instantaneous compression operation, wherein theDPCM encoding operation comprises: a delay operation of applying apredetermined delay amount to 1^(st) to (p−1)^(th) pixel values in eachdata block generated by the blocking operation, and outputting delayedpixel values; and a subtraction operation of calculating respectivedifferences between 2^(nd) to p^(th) pixel values in each data blockgenerated by the blocking operation and 1^(st) to (p−1)^(th) delayedpixel values outputted by the delay operation to generate (p−1)differential data as the differential data, and outputting the (p−1)differential data for the near-instantaneous compression operation, andwherein the near-instantaneous compression operation comprises: a bufferoperation of storing the (p−1) differential data outputted by the DPCMencoding operation; a level determination operation of generating thelevel value based on each of the (p−1) differential data outputted bythe buffer operation and outputting the level value, the level valuedetermining a bit to be deleted from each of the (p−1) differentialdata; and a data reduction operation of deleting the bit, as determinedby the level value outpuffed by the level determination operation fromeach differential data outputted by the buffer operation to generate(p−1) compressed differential data as the compressed differential data,and outputting the (p−1) compressed differential data for the packetassembling operation.